This is a competing renewal of a postdoctoral training program entitled Training in Investigative Infectious Diseases. The program is based in the Section of Infectious Diseases within the Department of Medicine at the Yale University School of Medicine. The program's overall goal is to produce exceptional physician-scientists and investigators who use modern laboratory research methods to study human infectious diseases. We expect to develop the next generation of infectious disease faculty at major universities that have the training and knowledge to span the gap between basic biology and issues in clinical infectious diseases. The program is designed primarily for M.D.'s and M.D./Ph.D.'s who have completed their subspecialty clinical training in the Infectious Diseases fellowship program at Yale, but selected M.D.s or M.D./Ph.D.s with clinical training in other fields will also be eligible to participate. The training faculty consists of 20 laboratory-based, and 9 translational researchers from 2 clinical (Medicine and Pediatrics) and 3 basic sciences departments (Microbial Pathogenesis, Immunobiology, and Microbial Diseases within the Department of Epidemiology and Public Health). The 3 major areas of research are (1) Innate Immunity and Microbes, (2) Vector-borne Diseases and (3) Molecular and Human Infectious Disease Pathogenesis. A primary mentor and co-mentor will supervise each trainee, and a training committee will monitor their progress. The trainees will have access to the newest programs and facilities at Yale, including working in the Anlyan Center for Medical Research and Education, The Boyer Center for Molecular Medicine, and/or participating in the Investigative Medicine Ph.D. program or Robert Wood Johnson Clinical Scholars program -- two novel programs designed specifically for M.D.s who have completed their clinical training. We are highly confident that this training program will provide its trainees with outstanding opportunities to pursue careers in investigative infectious diseases and bring a greater understanding of basic biological principles to current problems in medicine. This program will help train the next generation of infectious disease investigators at academic medical centers, with a focus on applying basic research to clinical medicine.